This invention relates to optical systems for projection displays and, in particular, relates to optical systems of the type disclosed in U.S. Pat. No. 5,552,922 (the ""922 patent), the contents of which are incorporated herein by reference.
The ""922 patent discloses a system for transmitting illuminating light from a light source to a digital light panel (DLP), and then from xe2x80x9conxe2x80x9d pixels of the DLP to a projection lens. Although the system of the ""922 patent works successfully, two areas in which that system can be improved to reduce its cost and make it easier to manufacture have been identified.
The first area relates to the tilted airspace between surfaces 18 and 20 of the ""922 patent. Because light from xe2x80x9conxe2x80x9d pixels passes through this airspace, the airspace can introduce astigmatism and coma into the projected image of the. DLP unless the width and wedge of the airspace are carefully controlled. The need for tight control of the width and wedge of the airspace makes manufacture of the system more difficult.
The second area involves the fact that in the system of the ""922 patent, light from xe2x80x9conxe2x80x9d pixels passes through both the optical component defined by surfaces 14, 16, and 18 of the ""922 patent and the optical component defined by surfaces 12 and 20 of that patent. This means that both of these optical components must be manufactured from high quality glass and must satisfy tight tolerances for surfaces flatness, surface positioning, straie, birefringence, and the like. Such requirements increase the overall cost of the system and are thus undesirable.
In view of the foregoing, it is an object of this invention to provide an improved optical system for transmitting illuminating light from a light source to a DLP and then from xe2x80x9conxe2x80x9d pixels of the DLP to a projection lens. More particularly, it is an object of the invention to provide a system of the general type disclosed in the ""922 patent which is easier to manufacture and has reduced cost.
To achieve these and other objects, the invention provides an optical system comprising a light source, a DLP, a projection lens, and a prism having first and second spaced apart surfaces wherein the first and second spaced apart surfaces, the light source, the DLP, and the projection lens are oriented relative to one another such that light from the light source passes through the first and second spaced apart surfaces to the DLP, light reflected from the xe2x80x9conxe2x80x9d or xe2x80x9cfirst positionxe2x80x9d pixels of the DLP is internally reflected at the second spaced apart surface towards the projection lens at an angle such that the light is within the acceptance angle of the projection lens, and light reflected from xe2x80x9coffxe2x80x9d or xe2x80x9csecond positionxe2x80x9d pixels of the DLP is either internally reflected at the second spaced apart surface towards the projection lens at an angle such that the light is not within the acceptance angle of the projection lens or otherwise passes through the prism so that the light is outside of the acceptance angle (see, for example, the uppermost bundle of light 41 in FIG. 3).